The present invention relates to a tape loading mechanism for VCRs (Video Cassette Recorders) adapted to withdraw a magnetic tape out of a tape cassette for winding it round a cylinder or to put the magnetic tape wound round the cylinder back into the tape cassette, and more particularly to a tape loading mechanism for VCRs which requires high reliability of operation.
For improved operability, VCRs are provided with tape loading mechanisms which automatically withdraw a magnetic tape out of a tape cassette for winding it round a cylinder (called "loading"), or to automatically put the magnetic tape wound round the cylinder back into the tape cassette (called "unloading"). The tape loading mechanism comprises, for example, a loading motor, a loading ring and a tape guide member. The tape guide member is composed of a tape guide unit coming into contact with the magnetic tape and a guide base for supporting the tape guide unit. When the loading ring is rotatably driven by the loading motor, the guide base of the tape guide unit coupled to the loading ring is moved such that the magnetic tape is withdrawn out of a tape cassette by the tape guide unit mounted on the guide base. When the guide base reaches a predetermined position close to the cylinder, it is fixedly held at that position. Specifically, two such guide bases are moved round the cylinder in opposite directions. When those two guide bases are positioned at their predetermined positions, the magnetic tape is in a loaded condition where it is helically wound round the outer peripheral surface of the cylinder over a range of predetermined angle. In the unloading operation, the two guide bases are moved in directions opposite to those in the loading operation, so that the magnetic tape is taken up by a reel in the tape cassette.
The tape guide unit, which is mounted on the guide base and comes into contact with the magnetic tape, comprises a guide roller and a tilt guide. Hereinafter, the guide base located on the upstream side of the cylinder (i.e., on the side where the magnetic tape running in the forward direction begins to contact with the cylinder) will be referred to as an upstream guide base, while the guide base located on the downstream side of the cylinder will be referred to as a downstream guide base.
The cylinder is mounted onto the chassis surface on a tilt. A tape lead portion for guiding the magnetic tape wound helically round the outer peripheral surface of the cylinder is tilted with respect to the chassis surface such that the inlet side becomes higher than the outlet side.
Under the condition where the upstream guide base has been positioned by a catcher in the predetermined position close to the cylinder, a running path of the magnetic tape from the tape cassette to the guide roller on the upstream guide base is made parallel to the chassis surface. To keep such parallel relation, the level of the magnetic tape is restricted by the guide roller. The tilt guide on the upstream guide base is inclined in a predetermined direction with respect to the chassis surface. The tilt guide is so inclined as to gradually descend the running path of the magnetic tape. This allows the magnetic tape to be contacted with the outer peripheral surface of the cylinder without any torsion, after it has come into contact with the tilt guide. Also, the magnetic tape is guided by the tape lead portion of the cylinder to run along the outer peripheral surface of the cylinder while being held at its lower edge against the tape lead portion without causing under forces.
Under the condition where the downstream guide base has been positioned by a catcher in the predetermined position close to the cylinder, the magnetic tape which has been so guided round the outer peripheral surface of the cylinder as to descend gradually by the tape lead portion, is converted in the running direction by the tilt guide on the downstream guide base such that it now ascends without any torsion. The guide roller on the downstream guide base makes the running path of the magnetic tape at the same level as that on the inlet side and the tape face vertical to the chassis surface. The magnetic tape is thereby taken up smoothly by the take-up reel in the tape cassette.
The upstream guide base and the downstream guide base are moved along predetermined guide paths as the loading rings revolve. In order to prevent damage of the magnetic tape, it is required that an attitude of the magnetic tape is kept stable during such movement as well.
If the force exerted on the magnetic tape during the course from start of the loading operation to end thereof is given by only a force acting in the lengthwise direction of the magnetic tape that is attributable to the force applied for withdrawing the magnetic tape from the tape cassette, the magnetic tape could be withdrawn from the tape cassette while keeping the same attitude as originally accommodated in the tape cassette. Under that condition, there occurs no problem such as damage of the magnetic tape.
However, because the tape lead portion of the cylinder is formed to be higher on the inlet side and lower on the outlet side, the attitude of the magnetic tape is forced to change during process of the loading operation. The magnetic tape first comes into contact with the outer peripheral surface of the cylinder when it is withdrawn out of the tape cassette for loading. Further, the magnetic tape successively comes into contact with the other tape guide members, causing the magnetic tape to be modified in its running path and restricted in its level. The attitude of the magnetic tape is thereby changed
If the attitude of the magnetic tape is changed during the loading operation in that way, the contact state of the magnetic tape against the tape guide member and the cylinder is also changed. This may damage the edge of the magnetic tape. In the case where a change in the attitude of the magnetic tape produces a force on the magnetic tape acting in the widthwise direction thereof, for example, the edge of the magnetic tape is strongly pressed against a flange portion of the guide roller. Since the magnetic tape has already been withdrawn from the tape cassette at the time of occurrence of such event, the edge of the magnetic tape is abraded and damaged by the flange portion of the guide roller.
Further, if the attitude of the magnetic tape is changed during the loading operation as mentioned above, the loading operation might be completed with such change left uncorrected. In this case, the magnetic tape is so offset to be ridden over the flange portion of the guide roller or the tape lead portion of the cylinder even after the loading operation. If the magnetic tape is run under that condition, the edge of the magnetic tape would be damaged In the case where the magnetic tape is lifted up away from the tape lead portion, a magnetic head may latch the edge of the magnetic tape during the recording or reproducing operation.
As will be apparent from the above explanation, the change in the attitude of the magnetic tape is a very important factor in respect of a level shift of the magnetic tape. It is therefore required to stabilize the attitude of the magnetic tape by reducing an amount of the level shift of the magnetic tape as well as smoothing the change of the tape level. As an attempt to achieve it, there is reported a paper written by Toshihiko Nakajima, et al., "Application of CAD to Development of VTR Mechanism System", Proceeding of the 5th Design Automation Engineering Lecture cosponsored by Japan Society of Mechanical Engineers and Japan Society of Precision Engineering (1987-7-9), pp. 28-30. This paper discusses the method of applying CAD (Computer Aided Design) to design of tape loading mechanisms for analyzing the attitude of a magnetic tape from the standpoint of a shift amount of the tape level, with a view to reduce the shift amount and smooth the change in the tape level for stabilizing the attitude of the magnetic tape.
In the VCRs which require very high reliability, such as VCRs for business use by way of example, it is important for the purpose of surely preventing damage of the magnetic tape that the tape loading mechanism is designed to make the shift amount of the tape level smaller than that in VHS-type VCRs for home use.
As explained above, in conventional VCRs, the upstream guide base is positioned close to the cylinder and the running path of the magnetic tape is modified by the tilt guide to direct downwardly such that the magnetic tape advances along the tape lead portion of the cylinder, during the loading operation. The downstream guide base is also positioned close to the cylinder to modify the running direction of the magnetic tape which is departed away from the cylinder to direct downwardly such that the magnetic tape ascends.
However, when the running direction of the magnetic tape is modified by the tilt guide in that way, there occurs a force for urging the magnetic tape to move in the axial direction of the tilt guide (i.e., in the widthwise direction of the magnetic tape). The widthwise movement of the magnetic tape due to such a force is restricted by the guide roller and the tape lead portion of the cylinder both of which serve to restrict the tape level. The above force produced by the tilt guide to move the magnetic tape in the widthwise direction thereof depends on such factors as an inclination of the tilt guide, a winding angle of the magnetic tape over the tilt guide, and a running speed of the magnetic tape. The larger the values of these factors become, the greater the force produced.
On the other hand, because of the difference in height between the inlet side and the outlet side of the tape lead portion of the cylinder, the tilt guide is required to make an abrupt conversion in the running direction of the magnetic tape. Therefore, the tilt guide is set to have a large inclination. In conventional VHS-type VCRs, since the running speed of the magnetic tape is relatively low during the loading operation, the aforesaid force tending to move the magnetic tape in the widthwise direction thereof has not become serious.
However, in those models of VCRs that the magnetic tape runs at a relatively high speed, such as high-vision VCRs and VCRs for business use, the force produced by the tilt guide for moving the magnetic tape in the widthwise direction thereof becomes very large during the reproducing step for search, in particular. The contact force of the magnetic tape against the flange portion of the guide roller and the tape lead portion of the cylinder is increased, resulting in a problem that the edge of the magnetic tape may be damaged.
Further, conventional tape running systems and tape loading mechanisms for VCR are known as disclosed in JP-U-59-194153 and an article in VIDEO SALON, "Fundamental Knowledge of Video", (1989, Vol. 4, p.40), for example.
In these magnetic recording and reproducing devices, a cylinder is mounted onto a chassis surface via a cylinder base on a tilt. A tape lead portion is provided on the outer peripheral surface of the cylinder for guiding the magnetic tape helically wound.
After the magnetic tape has been withdrawn out of a tape cassette, guide bases are positioned in their predetermined positions close to the cylinder by respective catchers provided integrally with the cylinder base. Under this condition, the running path of the magnetic tape from the tape cassette to the guide rollers on the guide bases is kept parallel to the chassis surface. Thus, in order to allow the magnetic tape to be contacted with the outer peripheral surface of the cylinder without any torsion, the guides are mounted on the guide bases so as to tilt in the predetermined directions with respect to the chassis surface.
In addition, the guide bases are provided with tilt surfaces on which the tilt guides are to stand upright, respectively.
As described above, the prior art requires at least three different tilt surfaces; i.e., the tilt surface of the cylinder base on which the cylinder is to be mounted, the tilt surface of the guide base on the inlet side of the cylinder, and the tilt surface of the guide base on the outlet side of the cylinder.
In the prior art, therefore, manufacture of parts having those tilt surfaces has been accompanied by difficulties in point of ensuring the required part accuracy, and the complexity of part configurations has also pushed up the cost.
Particularly, in high-vision VCRs and VCRs for business use, since the magnetic tape is run at a relatively high speed, the various guides are required to meet higher accuracy in assembly.